As a method for bonding electronic components such as semiconductor elements to a substrate, there is a bonding method using solder. The bonding method using solder has advantages, for example, in that electronic components can be bonded in a short time, in that solder has high reliability for thermal strain that occurs in connection with temperature change, and in that multiple electronic components can be bonded at one time by reflow.
However, the bonding method using solder has disadvantages, for example, in that it is difficult to bond multiple electrode terminals of electronic components at fine intervals, and in that solder has a low electric conductivity and thermal conductivity compared to silver and the like.
Meanwhile, as a method for bonding electronic components to a substrate, there is a method by solid-phase diffusion bonding, in which a heating or compressing is performed or an ultrasonic vibration is applied so that the bonding is performed (see Japanese Patent Laid-Open No. 2010-118534, for example).
The method by solid-phase diffusion bonding, which is a bonding method utilizing the atom diffusion phenomenon occurring between metals (electrodes) that do not melt by the heating or compressing under certain conditions, is generally performed under the condition of a few hundred degrees Celsius that is lower than the melting point of solder, and allows the temperature in bonding operation to be lowered relative to the bonding method using solder.
As such a method by solid-phase diffusion bonding, for example, there are a method of directly bonding the electrode terminals of electronic components and the electrodes of a substrate by applying a predetermined temperature and pressure, and a method of applying a metal fine powder paste between the electrode terminals of electronic components and the electrodes of a substrate and then bonding them by sintering the metal fine powder paste.
The method by solid-phase diffusion bonding has an advantage of making it possible to ensure a high electric conductivity and thermal conductivity while having a good thermal resistance. Therefore, the solid-phase diffusion bonding is a bonding method that can be particularly used not only in next-generation power semiconductors such as SiC (silicon carbide) and GaN (gallium nitride), which require a good thermal property and electric property, but also in a wide range of fields such as the connection of high-brightness LEDs (Light Emitting Diodes) and the bonding in LSIs (Large Scale Integrations).
Meanwhile, the solid-phase diffusion bonding has a disadvantage that it requires a high pressure, and for sufficiently developing diffusion reaction, requires more time than the bonding time by solder.
By the way, in many cases, multiple electronic components are bonded to a substrate. In bonding of multiple electronic components, the electronic components sometimes have different heights. In such cases, according to a conventional solid-phase diffusion bonding, the individual electronic components are respectively sandwiched between separate heaters, and a predetermined temperature and pressure are applied to each of the individual electronic components for a certain time.
However, the method in which the individual electronic components are sandwiched between separate heaters and a predetermined temperature and pressure are applied for a certain time has problems in that heaters for heating, motors for compressing and the like are required for each of the individual electronic components, resulting in an increase in production costs of a component bonding apparatus (bonder), and in that a lot of time is also required for diffusion reaction, resulting in a low productivity.
Further, in the multiple electronic components to be bonded to the substrate, the parallelisms are not equal as well as the heights. For uniformly compressing the multiple electronic components to bond them to the substrate, advanced controls such as the adjustment of the parallelisms are required, resulting in a decrease in productivity, as well.
Furthermore, the downsizing of electronic equipment and the like in recent years leads to a high requirement for the downsizing of the substrate, and the distance between the electronic components to be bonded to a single substrate, and the pitch between the terminals of the electronic components tend to be shortened. However, a large arrangement space is required in order to arrange heaters for heating each of the individual electronic components, motors for compressing and the like. Therefore, the method in which the individual electronic components are sandwiched between separate heaters and a predetermined temperature and pressure are applied for a certain time has also a problem in that it is difficult to bond the electronic components when the distance between the electronic components or the pitch between the terminals of the electronic components is short, resulting in an obstacle to the downsizing of the substrate.
Meanwhile, as a conventional method in which multiple electronic components with different heights are bonded to a substrate by solid-phase diffusion bonding, there is a method in which the multiple electronic components are arranged in liquid and then are bonded by compressing the multiple electronic components by the hydrostatic pressure of the liquid on heating of the liquid (see Japanese Patent Laid-Open No. 2012-89740, paragraphs 0044, 0046 and others).